Receiving apparatus for communication systems



Oct. 12, 1937.

A. J. SORENSEN RECEIVING APPARATUS FOR COMMUNICATION SYSTEMS Fi led Jan. 19, 1957 IN TOR P M A HIJ ATTORNEY Patented Oct. 12, 1937 T OFFICE RECEIVING APPARATUS FOR COMMUNI- CATION SYSTEMS Andrew J. Sorensen, Edgewood, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application January 19, 1937, Serial No. 121,322

6 Claims.

My invention relates to receiving apparatus for communicationsystems, and particularly to receiving apparatus for communication systems which provide a carrier telephone current for telephone communication and a current equivalent to the carrier modulated with a predetermined voice frequency for calling and code signaling.

A feature of my invention is the provision of novel and improved apparatus for systems of the type here involved wherewith the receiving apparatus is normally conditioned for reception and is efiective to reduce noise and eliminate interference. Other features and advantages of my invention will appear as the specification progresses.

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in claims.

Apparatus embodying my invention is particularly useful for communication systems for railway trains where amodulated carrier current is received at a station located on a vehicle of a trainthrough the medium of circuit elementscoupled with the track rails, such circuit elements preferably including an inductor coil mounted on the vehicle in inductive relation with the track rails. Such modulated carrier current is supplied to the track rails in multiple and "news therein in both directions from the point at which 'it is supplied to the rails in the wellknown manner. Heretofore the receiving apparatus has been normally conditioned for reception in order that code signaling may be effected and telephone communication may be initiated without any act on the part of the operator at the station on the'vehicle. Since the receiving apparatus is normally conditioned for reception, earth currents and stray magnetic fields, as well 'asother unwanted energy, may create a noise at the loud speaker or telephone receiver during non-communication periods, this noise being amplified due to the fact that the receiving apparatus includes a high-gain amplifier, as well as a demodulator. As a matter of fact, the noise may be due in part to disturbances created within the high-gain amplifier itself. In my present invention, I provide a filter-relay combination which is interposed between the output side of the amplifier-demodulator and the loud speaker and which is proportioned and adjusted to normally pass'only the frequency corresponding to the predetermined frequency with which the carrier is modulated to'produce the code signaling or calling current. -Hence, only a few cycles of unwanted energy to each side of said predetermined frequency are effective to operate the loud speaker and produce a noise during non-communicating periods. During telephone communication the filter is by-passed by taking the microphone off the hook or some similar control by the operator at the called station, and the full range of voice frequencies resulting from demoduation of the carrier telephone current is applied to the loud speaker without attenuation.

For a better understanding of my invention, reference may be had to the accompanying drawing, which is a diagrammatic view of one form of apparatus embodying my invention.

Referring to the drawing, the reference character IC designates an inductor coil such as may be mounted in inductive relation with a transmitting circuit, not shown. For example, when the receiving apparatus is installed on a vehicle of a railway train, the inductor coil 10 would be mounted on the vehicle in inductive relation with the track rails. In other words, the inductor coil IC is disposed for inductively receiving an electromotive force in response to a modulated carrier currentflowing in a transmitting circuit. The

opposite terminals of the inductor coil 10 are connected over wires l and 2 with the input side of an amplifier-demodulator AD.

The amplifier-demodulator AD may be any one of several well-known types capable of amplifying and demodulating a carrier telephone current and a code signaling current which is an equivalent of the carrier modulated with a predetermined voice frequency. The amplifierdemodulator AD is shown conventionally only for the sake of simplicity, since the specific structure of this device forms no part of my invention. The output side of the amplifier-demodulator AD is connected with the primary winding 3 of an output transformer T. Consequently, the frequencies resulting from demodulation of current picked up by the inductor IC appear in the current flowing in the primary winding 3 and are effective to induce an electromotive force of corresponding frequencies in the secondary winding l of the transformer T.

The electromotive forces induced in the secondary winding 4 of transformer T are applied to an operating winding 5 of a loud speaker LS over a filter-relay circuit means, the essential elements of which consist of a reactor Bl, a condenser Cl and a' relay R. With the relay R energized closing its front contacts 6 and If), two circuits are closed, a first one of which may be traced from the top terminal of secondary windand wire 8 to the lower terminal of secondary winding 4. A second circuit may be traced from the lower terminal of the operating winding 5 of loud speaker LS over wire 9, front contact ill of relay R, a portion -3 of the winding of th reactor RI, and wire I! to the upper terminal of the operating winding 5. Due to the coupling between the portions AB and C'B of the winding of the reactor RI, the current flowing in the first traced circuit as a result of the electromotive force induced in the secondary winding 4 of winding of the reactor RI consists of a portion DC, as well as the two portions A-B and C--B. The condenser 01 is connected across the full winding of the reactor RI. The condenser CI and the reactor RI are so proportioned that the circuit consisting of the condenser CI and the full winding of reactor RI istuned to resonance at the predetermined frequency of the calling or code signaling current. The two portions AB and C-B of the reactor winding are adjusted to give as nearly as possible the amount of filtering action required, with an energy loss not greater than can be tolerated. The portion D-C of the reactor winding is adjusted to permit the use of a relatively small size condenser.

When the relay R is deenergized closing its back contacts I2 and I3, a third circuit may be traced from the top terminal of the secondary winding 4 of transformer T over wire I, back contacts I2 and I3 of relay R in series, wire 9, operating winding 5 of the loud speaker LS and wires I I and 8 to the lower terminal of the secondary winding 4. It is to be noted that this third circuit by-passes the filter including the reactor RI and the condenser CI.

.The relay R is normally energized over a simple circuit including a circuit controlling contact I4. As here shown, the contact I4 is operatively connected with the microphone M of theassociated *transmitting apparatus, the arrangement being in the drawing by the dotted lines.

It follows that normally the relay R is ener- "gized and the filter-relay circuit combination is conditioned to pass only the predetermined frequency of the code signaling current, with the result that noise is reduced during the noncommunicating periods and interference from nearby transmission and communication systems is substantially eliminated, However, code sig- 7 naling current picked up by the inductor coil 10 posed between the transformer T and the loud speaker LS is by-passed so that the full range of voicefrequencies resulting from demodulation of the carrier telephone current is applied to the loud speaker without attenuation. At the termination of telephone communication the operator would replace the microphone on the hook and in so doing would close the contact I4 and reenergize relay R, which on picking up would restore the apparatus to its normal condition.

Although apparatus embodying my invention is specifically adaptable to communication systems for railway trains, it will be understood that the invention is not limited to this one use and many places will suggest themselves where it will be useful.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of 'my'invention.

Having thus described my invention, what'I claim is: a

1. In combinatiom'receiving apparatus including an amplifier-demodulator capable of amplifying and demodulating carrier communication current having a given range of signaling fre- I quencies, a'transformer having a primary winding connected to the output side of the amplifierd-emodulator to receive the signaling frequencies resulting from demodulation, a signaling device responsive to such range of signaling frequen cies, a filter including a reactor provided with a (-335 said secondary winding and. said operating winding; and a control relay having contacts interposed in said first, second and third circuits for selectively governing said circuits. I 2. In combination, receiving apparatus including an amplifier-demodulator capable of amplifying and demodulating a carrier telephone current, a transformer having'a primary winding connected to the output side of said amplifierdemodulator to receive the voice frequencies resulting from demodulation, a loud speaker, a.

filter including a reactor and a condenser and adjusted to resonance at a predetermined voice frequency, a first circuit including a secondary winding of the transformer and a. first portion of the winding of said reactor,.a second circuit including anoperating winding of said loud speaker and a second portion of the winding of said reactor, a third circuit including said secondary winding and said operating winding; and a control relay having contacts interposed in said first, second and third circuits for selectively governing said circuits.

3. In combination, receiving apparatus including an amplifier-demodulator capable of amplifying and demodulating a carrier telephone current, a control winding coupled with the output side of said amplifier-demodulator to receive the voice frequencies resulting from demodulation, a loud speaker, a relay, a reactor provided with a winding, a condenser, means to connect said condenser across the winding of said reactor to form a circuit adjusted to resonance at a predetermined voice frequency, means including a front contact of said relay to connect said control winding across a first portion of the winding of the reactor, means including another front contact of said relay to connect an operating winding of said loud speaker across a second portion of the winding of the reactor, means including a back contact of said relay to connect said control winding across said operating winding of the loud speaker, and means including another contact to control said relay.

4. In combination, receiving apparatus including an amplifier-demodulator capable of demodulation of a carrier telephone current and a code signaling current which is the carrier modulated by a predetermined voice frequency and which apparatus is normally conditioned for reception, a control winding coupled with the output side of said amplifier-demodulator to receive the frequencies resulting from demodulation, a loud speaker, a relay, a reactor provided with a winding, a condenser connected across the reactor winding to form a filter adjusted to resonance at said predetermined voice frequency, a first circuit including a front contact of the relay as well as said control Winding and a first portion of said reactor winding, a second circuit including a front contact of said relay as well as an operating winding of the loud speaker and a second portion of the reactor winding for sounding the code signaling current with frequencies outside of said predetermined frequency suppressed, a third circuit including aback contact of said relay as well as said control winding and said operating winding of the loud speaker to reproduce the voice frequencies of said telephone current, and a circuit including a normally closed manually operable contact for controlling said relay.

5. In combination, receiving apparatus including an amplifier-demodulator capable of demodulating a carrier telephone current and a code signaling current which is the carrier modulated by a predetermined voice frequency and which apparatus is normally conditioned for reception, a control winding coupled with the output side of said amplifier-demodulator to receive the frequencies resulting from demodulation, a loud speaker, a relay, a filter including a reactor and a condenser and adjusted to resonance at said predetermined voice frequency, a first circuit means including a front contact of said relay to connect said control winding with an operating winding of the loud speaker with said filter interposed between said two windings, a second circuit means including a back contact of said relay to connect said control winding with said operating winding with the filter by-passed, and a control circuit including a normally closed manually operable contact for controlling said relay.

6. In combination, receiving apparatus including an amplifier-demodulator capable of demodulating a carrier telephone current and a code signaling current which is the carrier modulated by a predetermined voice frequency and which apparatus is normally conditioned for reception, a control winding coupled with the output side of said amplifier-demodulator to receive the frequencies resulting from demodulation, a loud speaker, a filter including a reactor and a condenser and adjusted to pass said predetermined frequency and to substantially suppress frequencies on each side of said predetermined frequency, a first circuit means to connect said control winding with an operating winding of the loud speaker with said filter interposed between said two windings, a second circuit means to connect said control winding with said operating winding with said filter by-passed, and a relay having contacts interposed in said first and said second circuit means for selectively governing said two circuit means.

ANDREW J. SORENSEN. 

